Heart valve replacement surgeries have been performed in human beings for many years. Most frequently, these valve replacement procedures are utilized to replace the mitral or aortic valves of patients who suffer from valvular heart disease.
In particular, surgical replacement of the aortic valve has proven to be a successful mode of treatment of patients who are diagnosed with a) obstruction (i.e., stenosis) of the aortic valve or b) leakage (i.e., regurgitation, incompetence or insufficiency) of the aortic valve. In some patients, symptoms of both obstruction and leakage are present, this being known as "mixed disease" or "combined lesions". These types of aortic valvular heart disease may be caused by a number of factors, including congenital deformations, infections, degenerative calcification, and certain rheumatological disorders.
Surgical replacement of the aortic valve is typically performed under general anesthesia, with full cardiopulmonary bypass. An incision is made in the aorta adjacent to the heart, and the leaflets of the endogenous aortic valve are removed along with any calcified surrounding tissue, thereby creating an annular opening (i.e. the "aortic annulus") at the site previously occupied by the endogenous aortic valve. Thereafter, a prosthetic aortic valve is selected and sutured into the aortic annulus, as a prosthetic replacement for the surgically-removed endogenous valve.
The available types of prosthetic aortic valves have heretofore included mechanical valves as well as valves formed of preserved animal tissue (i.e., "bioprosthetic" valves). Of the bioprosthetic valves, some (known as "stented" bioprosthetic valves) incorporate a man-made stent or support frame upon which the preserved biological tissue is mounted. Others (known as "stentless" bioprosthetic valves) do not include any man-made stent or support frame, and are formed entirely of preserved biological tissue.
Tissues for use in bioprosthetic heart valves are typically harvested from the hearts of donor animals and such tissues typically contain large amounts of connective tissue proteins (e.g., collagen and elastin). After the desired tissues have been harvested from the donor animals, they undergo a chemical "fixing" process wherein the connective tissue proteins within the tissue are exposed to one or more chemical cross linking agents capable of forming chemical cross linkages between amino groups present on the connective tissue protein molecules. The types of chemical cross linking agents useable for this purpose include: formaldehyde, glutaraldehyde, dialdehyde starch, hexamethylene diisocyanate and certain polyepoxy compounds.
Examples of commercially available stented bioprosthetic valves include the CarpentierEdwards.RTM., PERIMOUNT.TM. Pericardial Bioprosthesis (Baxter Healthcare Corporation, Edwards CVS Division, Post Office Box 11150, Santa Ana, Calif. 92711-1150) as well as the Carpentier-Edwards.RTM. Porcine Bioprosthesis (Baxter Healthcare Corporation, Edwards CVS Division, Post Office Box 11150, Santa Ana, Calif. 92711-1150).
Examples of commercially available stentless bioprosthetic valves include the Edwards Prima.TM. Stentless Bioprosthesis (Baxter Edwards AG, Spierstrasse 5, CH-6848 Horw, Switzerland), the Medtronic Freestyle.TM. Aortic Root Bioprosthesis (Medtronic, Inc. 7000 Central Avenue NE, Minneapolis, Minn. 55432-3576) and the St. Jude Toronto.TM. SPV Stentless Bioprosthesis (St. Jude Medical, Inc. One Lillehei Plaza, St. Paul, Minn. 55117).
The stentless bioprosthetic valves may offer superior hemodynamic performance when compared to their stented counterparts, due to the absence of flow restrictions which can be created by the presence of a stent and/or sewing ring. Also, the stentless bioprosthetic valves may exhibit better post-implantation durability than the stented bioprosthetic valves, because they provide a more flexible structure which serves to dissipate stress during the cardiac cycle.
At least one of the previously available aortic bioprostheses (i.e., the Medtronic Freestyle.TM. Aortic Root Bioprosthesis referred to hereabove) has included a segment of the donor animal's ascending aorta, along with ligated remnants of the donor's coronary arteries extending outwardly therefrom. However, because the coronary artery remnants included in this bioprosthesis have been ligated prior to fixation, the lumens of these coronary artery segments are substantially collapsed and occluded. As a result, it is typically necessary for the surgeon to trim away a substantial portion of each coronary artery remnant, prior to anastomosis of the patient's endogenous coronary arteries thereto.
It is desirable to devise a new stentless aortic bioprosthesis which includes coronary artery remnants which have been fixed in an unligated, natural configuration, such that the lumens of such coronary artery remnants remain patent, and the patient's endogenous coronary arteries may be anastomosed directly thereto.